OWN PRODUCT · IN PRODUCTION · 2026

A finance app thatforecasts instead ofreporting.

PRODUCT: Monark
ROLE: Everything
STACK: Next.js · TS
DATA: Postgres · Prisma
HOST: Vercel

01 THE PROBLEM

Budget apps report the past. Nobody needs a report.

Every personal finance tool I tried answered the wrong question. They tell you what you spent, in a chart, after the fact. The question that actually matters on day four of the month is whether you are on track to end it badly.

So Monark's dashboard does not open with a chart. It opens with a sentence: your net position and where the month is pacing to. The visualisation is secondary to the statement.

The design constraint I set: if the headline needs a legend to be understood, it is wrong.

02 ARCHITECTURE

Deliberately small.

One Next.js app, one Postgres database, Prisma between them. No microservices, no message bus, no event sourcing. A single-user finance app does not need distributed anything, and every extra moving part is something that can be down at 2am for no revenue.

FIG. 02.1 / SYSTEM

CLIENT
next.js

SERVER ACTIONS
user-scoped

PRISMA
typed

POSTGRES
source of truth

EVERY TOTAL IS DERIVED ON READ, NOTHING IS CACHED OR ROLLED UP

NO QUEUE, NO CRON, NO SECOND COPY OF A NUMBER

03 DATA MODEL

Constraints in the schema, not in the app.

Anything the database can guarantee, the database guarantees. Application code is where rules go to be forgotten.

transactions

Amounts in minor units as bigint, with an income or expense type rather than a sign. Category is a foreign key, never a string.

budgets

Unique on user, category and month, so two budgets cannot fight over the same month and the database is what says so.

recurring_transactions

A template plus the last month it was advanced past, so confirming or skipping a month is idempotent and a missed run cannot double-post.

goals

Target plus optional deadline. Progress is summed from contributions, never stored, because stored progress goes stale silently.

04 STACK MANIFEST

CLIENT

Next.js · React · TypeScript · Tailwind

SERVER

Node · Server Actions · NextAuth · bcrypt

DATA

Postgres · Prisma · pg

SERVICES

Vercel · Resend · Gemini

Want this level of thinking on your product?

chris@christopheryu.com →BOOK 30 MINUTES →